Implant Placement Planning

ABSTRACT

A method of planning a procedure to fasten an implant to a bone includes displaying a model of the bone and a model of the implant on a display device. The model implant is positioned on the model bone in a desired implant position. A first boundary volume of a first fastener configured to fasten the prosthesis to the bone is also displayed on the display device. The first boundary volume represents a range of possible positions that the first fastener may have with respect to the prosthesis when fastened to the bone. The boundary volume may be used to determine a desired size, shape, and/or positioning of the fastener with respect to the bone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/529,928, filed Aug. 2, 2019, which is a continuation of U.S. Pat. No.10,405,926, filed on Aug. 10, 2018, which is a continuation of U.S. Pat.No. 10,070,928, filed on Jul. 1, 2015, the disclosures of which are allhereby incorporated by reference herein.

BACKGROUND

The present disclosure relates generally to orthopedic prostheses. Inparticular, the present disclosure relates to planning the size, shape,position, and/or orientation of an implant relative to a patient'sanatomy or another implant.

Orthopedic knee implant systems have been used for many years to treatpatients with knee joints that have been damaged by trauma or disease,such as osteoarthritis, rheumatoid arthritis, and avascular neurosis. Aknee arthroplasty procedure generally involves resecting, cutting, orresurfacing the damaged sections of the knee and replacing them with anendoprosthesis or implant.

Most knee implant systems are tricompartmental or total implants and thesurgical procedure used with such implants is commonly known as totalknee arthroplasty. These implants are known as tricompartmental implantsbecause they are used when the knee joint is prepared to receive animplant by resurfacing or resecting the three articulating compartments,i.e., the medial and lateral femorotibial and the patellofemoralsurfaces. Regardless of the type of implant used, arthroplastiesgenerally require the bone to be specifically prepared to receive acorresponding implant by resecting, cutting, resurfacing, or otherwisedeforming the bone to accept the implant.

Unicondylar or unicompartmental knee implants have become of greatinterest in the orthopedic industry due to their less invasive naturewhile providing the option of maintaining healthy knee compartments ifpresent in the knee joint. Unicondylar knees typically resurface orresect the medial or lateral femorotibial articulating surfaces thusallowing preservation of the other compartments not suffering fromdamage due to trauma or disease.

Historically, orthopedic devices have been mated with host bone bycementing them in place using methyl methacrylate, generally termed bonecement. The use of bone cement in attaching a prosthesis within or ontoa prepared bone provides an excellent immediate fixation but has variousdisadvantages that may appear over time. Physical loads are repeatedlyapplied to the implant over its life. If bone cement is used to secure aunicompartmental knee prosthesis, the bone cement may fatigue andfracture under the repeated loading. In some instances, degradation ofthe bone cement integrity may cause the device to become loose, therebynecessitating replacement. Old bone cement must be removed from the hostbone as part of the implant replacement procedure. This procedure can becomplex, time consuming and potentially destructive to healthy bonestructures surrounding the implant. Furthermore, conventional bonecement is cured after it has been dispensed into the patient's joint.Loose undetected cement fragments can remain in the joint space and,with patient mobility over time, increase the degradation rate ofarticulating implant surfaces.

More recently, the development of orthopedic implant designs has movedtowards satisfying the requirements of high demand patients. Patientstoday require more from their implants, and because patients are livinglonger, they require implants that to last longer. Accordingly,developments have been made in materials used to make orthopedicimplants to improve implant longevity, such as highly porous metals thatimprove biological bone fixation. These implants are generally termedpress-fit or cementless.

Recognizing the disadvantages of cement fixation techniques, prior artdevices have also been developed that utilize other mechanicalattachment means to join an implant to bone for immediate stabilization.Although various implant surface treatments intended to bond with bonebiologically for long term stable attachment have proven successful, aninitial fixation and stabilization is required before the bone growthcan occur. One technique of mechanically securing an implant is to affixit to the bone with screws, or other mechanical fasteners. However, dueto the nature of the bone surrounding the surgical site, and otherlimiting factors such as artery location and the like, it is desirableto insert the screw(s) into the bone with optimal trajectories.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the disclosure, a method of planning aprocedure to fasten an implant to a bone comprising includes displayingon a display device a model of the bone. A model of the implant is alsodisplayed on the display device. The model implant is positioned on themodel bone in a desired implant position. A first boundary volume of afirst fastener configured to fasten the prosthesis to the bone isdisplayed on the display device. The first boundary volume represents arange of possible positions that the first fastener may have withrespect to the prosthesis when fastened to the bone. The first boundaryvolume may have a plurality of volume portions such that each volumeportion represents possible positions of a different sized firstfastener. A first fastener size that has a boundary volume positionedentirely within the model bone may also be provided. The step ofdisplaying the model bone may include displaying bone qualityinformation, such as bone density, on the model bone. A second boundaryvolume representing a second range of possible positions of a secondfastener configured to couple the prosthesis to the bone may also bedisplayed on the display device. An overlap volume defined by volumeoccupied by both the first and second boundary volumes may be indicatedon the display.

According to a further aspect of the disclosure, a method of planning aprocedure to fasten an implant to a bone includes displaying on adisplay device a model of the bone and a model of the implant having atleast one aperture for receiving a fastener. The model implant ispositioned on the model bone in a desired implant position. A firstboundary volume of a first fastener configured to fasten the prosthesisto the bone is also displayed on the display device. The first boundaryvolume represents a range of possible positions that the first fastenermay have when fully received within the at least one aperture. The firstboundary volume may have a plurality of volume portions such that eachvolume portion represents possible positions of a different sized firstfastener. A first fastener size that has a boundary volume positionedentirely within the model bone may be provided. The step of displayingthe model bone may include displaying bone quality information, such asbone density, on the model bone. A second boundary volume representing asecond range of possible positions of a second fastener configured tocouple the prosthesis to the bone may also be displayed. An overlapvolume defined by volume occupied by both the first and second boundaryvolumes may be indicated on the display. The prosthesis may be a tibialimplant or a bone plate

According to yet another aspect of the disclosure, a computer systemincludes at least one processor configured to execute instructions todisplay a model of a bone and a model of an implant on a display device,and to change a position of the model implant on the model bone to adesired implant position in response to user input. The processor mayalso be configured to display on the display device a first boundaryvolume of a first fastener configured to fasten the implant to the bone,the first boundary volume representing a range of possible positionsthat the first fastener may have with respect to the prosthesis whenfastened to the bone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top perspective view of a unicondylar tibial implantassembly.

FIG. 1B is a bottom perspective view of the unicondylar tibial implantof FIG. 1.

FIG. 2A is a side view of the unicondylar tibial implant of FIG. 1.

FIG. 2B is a bottom view of the unicondylar tibial implant of FIG. 1.

FIG. 3A is a side view of the unicondylar tibial implant of FIG. 1 witha bone screw positioned within a through hole of the tibial implant.

FIG. 3B is a rear view of the assembly of FIG. 3A.

FIG. 4 is a schematic side view of the tibial implant assembly of FIG. 1with ranges of potential screw volume occupancies illustrated.

FIGS. 5A-D show different views of a model tibia implants overlaid on amodel tibia.

FIG. 6 is a schematic representation of a pre-operative planning system.

FIG. 7A is a highly schematic view of an operative step of drilling intothe tibia.

FIG. 7B is a highly schematic view of a navigation system illustratingthe procedure of FIG. 7A.

FIG. 8A is a highly schematic view of a proximal humerus.

FIG. 8B is a highly schematic view of a bone plate.

FIG. 8C is a highly schematic view of the bone plate of FIG. 8Bimplanted onto the humerus of FIG. 8A.

FIG. 8D is a schematic view of the bone plate of FIG. 8B positioned onthe humerus of FIG. 8A, with ranges of potential screw volumeoccupancies illustrated.

FIG. 8E illustrates volumes of potential screw interference for thesystem illustrated in FIG. 8D.

DETAILED DESCRIPTION

When referring to specific directions in the following discussion ofcertain implantable devices, it should be understood that suchdirections are described with regard to the implantable device'sorientation and position during exemplary application to the human body.Thus, as used herein, the term “proximal” means closer to the heart andthe term “distal” means more distant from the heart. The term “inferior”means toward the feet and the term “superior” means toward the head. Theterm “anterior” means toward the front of the body or the face and theterm “posterior” means toward the back of the body. The term “medial”means toward the midline of the body and the term “lateral” means awayfrom the midline of the body. Also, as used herein, the terms “about,”“generally,” and “substantially” are intended to mean that slightdeviations from absolute are included within the scope of the term somodified. Likewise, for purposes of convenience and clarity only,directional terms such as top, bottom, above, below and diagonal, may beused with respect to the accompanying drawings. Such directional termsused in conjunction with the following description of the drawingsshould not be construed to limit the scope of the invention in anymanner not explicitly set forth. Additionally, the term “a,” as used inthe specification, means “at least one.” The terminology includes thewords above specifically mentioned, derivatives thereof, and words ofsimilar import.

Although much of the disclosure below is directed to screw length and/ortrajectory planning in connection with a unicondylar knee implant, itshould be understood that the implant size, shape, position, and/ororientation planning methods disclosed herein may be applicable to anysurgical procedure in which an implant, such as a screw (or pin, or likedevice) is to be implanted into a patient relative to another implant ora patient's anatomy, such as a bone, including in connection with otherbone implants, such as bone plates or joint implants, including otherknee implants and implants for other joints, such as ankle, shoulder andhip implants, for example. It should further be understood that the termtrajectory, as used herein, may generally refer to the three-dimensionalposition and/or orientation of an object, such as a screw, in space.

As noted above, partial knee implants, also known as unicondylar orunicompartmental knee implants, are designed to replace either a medialor lateral compartment of a knee joint. A unicondylar replacementassembly may include a tibial implant, either by itself or inconjunction with an implant designed to replace a femoral condyle. Thepreparation of the bone to accept such implants may be facilitated byinstrumentation such as bone files, burrs, saws, punches, computerand/or robot assisted instrumentation/navigation systems. Once the boneis prepared, the implant may be secured to the bone by different means,including bone cement which bonds to the implant and impregnates thebone resulting in fixation of the implant to the bone interface.

The present disclosure relates, at least in part, to methods and devicesfor facilitating fixation directly to the bone, i.e., without bonecement. Such fixation without bone cement is referred to herein ascementless fixation. The present disclosure addresses, among otherissues, the facilitation of planning and carrying out the fixation of animplant directly to bone with one or more screws or related fasteners,such as bone pins. It should also be noted that although the descriptionfocuses on cementless fixation, the concepts described herein may beused with bone cement, although it may not be necessary.

As noted above, the present disclosure relates to the planning of thesize, shape, position, and/or orientation of an implant to be implantedinto a patient relative to a patient's anatomy, such as a bone, and/orrelative to another implant. A first example of such planning isdescribed in relation to a partial knee arthroplasty (“PKA”) procedure,although other procedures employing the inventive methods are describedin more detail below. FIGS. 1A-D illustrate an embodiment of aunicondylar tibial implant 10 that may be fixed to a bone pursuant tothe concepts disclosed herein. Tibial implant 10 may generally include atibial tray or baseplate 20 and a bearing surface or member 30. Ofcourse, as noted above, although the concepts are described herein inconnection with a unicondylar implant for the tibia, the disclosure hasapplicability to other types of implants. The tibial implant 10 can beconstructed from any combination of solid metal, porous metal, polymersand/or other resorbable materials. For instance, it is contemplated toform the bearing 30 of a polymer material such as PEEK, and thebaseplate 20 of a metal such as titanium or stainless steel. Likewise,it is contemplated to form baseplate 20 of different materials, e.g., aporous portion of baseplate 20 may be formed of a different materialthan the remainder of the implant.

For purposes of convenience only, and not by way of limitation, theforegoing description of unicondylar tibial implant 10 will be describedand illustrated with respect to a unicondylar tibial implant 10 for amedial tibial condyle. However, the foregoing description and featuresof the unicondylar tibial implant 10 are equally applicable to aunicondylar tibial implant for a lateral condyle, such similar featuresof the lateral unicondylar tibial implant being substantially mirrorimages of such features of the medial unicondylar tibial implant. Ofcourse, it is also contemplated that the medial and lateral versions ofthe assembly may be of a different construction to accommodate thedifferent bony anatomy of the medial and lateral portions of the tibia.

The tibial implant 10 may be provided with a through-hole or aperture 40through which another device, instrument or material e.g., a locking ornon-locking bone screw 50 (as is shown in FIGS. 2A and 2B) can beinserted. The aperture 40 may be shaped and sized for the passage of thebone screw 50 through a superior aspect of the tibial implant 10 intothe bone beneath the underside or inferior surface of the baseplate 20.The aperture 40 may be fully or partially threaded or may not bethreaded. Aperture 40 may be designed with a ramp surface (not shown)such that the aperture may form a compression hole or may be designedsuch that the bone screw 50 can be angulated with respect to one or bothof the top surface 20 a and bottom surface 20 b of baseplate 20 toachieve a desired direction by the user. Such apertures 40 and bonescrews 50 are readily known in the art and a detailed description oftheir structure and operation is not necessary for a completeunderstanding of the present invention. It should further be noted that,although it is preferable to employ a separate bearing surface 30 on topof baseplate 20, for example to cover aperture 40 and a screw 50 seatedtherein, it is not necessary to employ a bearing surface 30 separatefrom baseplate 20.

The tibial implant 10 may employ the use of a knockout plug 42 formedwithin the aperture 40 and out of a material that is metallurgicallycontinuous with the greater bulk of the tibial implant 10. The knockoutplug 42 may be configured to be removed from the remainder of the tibialimplant 10 via a boundary shear section or weakened area 44 around theplug 42 (see FIG. 2B) upon the application of a suitable force. The plug42 may be machined into the baseplate 20 or built in final form throughan additive manufacturing process such as by direct metal lasersintering, for example. The aperture 40 may be obstructed by theknockout plug 42 so that the superior surface of the baseplate facingthe bearing component 30 is fully continuous without any path throughwhich debris or material could pass through the baseplate 20 to the boneengaging underside of the tibial implant 10. Thus, in the event ofbackside wear of the bearing component 30, wear particles are lesslikely to migrate out of the baseplate 20 than if an already presentaperture were in place. The knockout plug 42 can optionally include athreaded stud (not illustrated), which mates to instrumentation tofacilitate removal of the knockout plug 42.

In sum, the baseplate 20 has an initially covered aperture 40 into whicha screw 50 can be placed to stabilize the tibial implant 10 to theprepared bone upon implantation. Other unicondylar tibial implants aredescribed in greater detail in U.S. Patent Publication No. 2014/0277548,the disclosure of which is hereby incorporated by reference herein.

The aperture 40 of baseplate 20 may have a contoured shape. For example,the aperture 40 may take the form of a portion of a sphere or anotherrounded surface. Similarly, screw 50 may have a contoured head, such asa spherical or partially spherical head. Based on the particular shapesof the aperture 40 and the head of the screw 50, the screw 50 may have arange of possible angulation with respect to the tibial implant 10. Forexample, as shown in FIGS. 3A-B, the shaft of screw 50 may have a rangeof possible positions described by a volume generally in the shape of acone 52 (or a portion thereof).

It may be preferable to preoperatively plan the placement of screw 50with respect to the bone into which the screw will be inserted during animplantation procedure. For example, through preoperative or evenintraoperative planning, a surgeon may determine that a particular sizescrew 50 and/or particular angulation of the screw 50 is undesirable,for example because such positioning may result in a portion of thescrew 50 being positioned to close to the cortical wall or shell of abone, or even penetrating beyond the cortical shell of the bone. Avariety of additional variables and methods may be used topreoperatively or intraoperatively plan a desired length and/ortrajectory of one or more screws relative to an implant and bone towhich the implant is to be secured, for example including the tibialimplant 10 system described above. For example, the position of aperture40 with respect to baseplate 20 and the position of baseplate 20 withrespect to a bone 70 may also be used to preoperatively orintraoperatively plan a desired length and/or trajectory of one or morescrews. Other variables such as bone quality, patient morphology andkinematics, for example, may also be used in screw planning.

Although much of the disclosure is generally described in relation tothe use of tibial implant 10 on a patient's tibia, it should be clearthat the concepts described herein may apply with equal force to otherbone implants secured to bone with a bone screw or other fastener, suchas acetabular cups of hip implants, or bone plates fastened to a longbone.

For a particular type of screw 50 and tibial implant 10, a number ofvariables may determine the entire volume which the screw 50 maypotentially occupy. For example, FIG. 4 provides a simplifiedrepresentation tibial implant 10 and volumes that may be occupied bydifferent screws. For example, the entire volume that may be potentiallyoccupied by a screw 50 assembled to the baseplate 20 of tibial implant10 may be determined by two factors: (1) the length of the shaft ofscrew 50; and (2) the shape of the head of screw 50 and thecorresponding shape of the aperture 40 of the baseplate 20. In otherwords, the length of screw 50 and potential angulation of screw 50 withrespect to baseplate 20 may define a particular volume that may beoccupied by screw 50, whereas the position of that particular volumewith respect to the bone may be determined by the placement of baseplate20 with respect to the bone and the position of aperture 40 with respectto baseplate 20. Based on these or other factors, a preoperative plan,which may for example be displayed on a computer display or other visualmedium, a representation of tibial implant 10 and the volume that avariety of screws of different sizes may occupy may be simultaneouslydisplayed. For example, FIG. 4 shows the tibial implant 10, a firstvolume 52A that a relatively short screw may occupy, a second volume 52B(which includes volume 52A) that a screw of medium length may occupy,and a third volume 52C (which includes volumes 52A and 52B) that arelatively long screw may occupy. Volume 52A may define a cone of volumethat could be occupied by a 15 mm screw, while volume 52B defines a coneof volume that could be occupied by a 25 mm screw, and volume 52Cdefines a cone of volume that could be occupied by a 35 mm screw. Itshould be understood that these three sizes of screws are merelyprovided as examples. In addition, other types of implant and/or screwshapes may be taken into account. Similarly, although the term “cone” isgenerally used in relation to the volume that the screw may occupy, thevolume is more precisely frustoconical, although the volume need notmeet the precise mathematical definition of a cone or frustocone, andthe precise shape of the volume depends on the characteristics of screw50 and the aperture 40. Further, it should be noted that the volumesdisplayed preferably represent positions of screw 50 when the screw isan in implanted position, for example when the head of the screw isfully seated into the aperture 40 of the baseplate 20 or when the screw50 is otherwise fully received in the aperture 40.

The representation of the tibial implant 10 and the volumes 52A-C thatmay be occupied by the screw 50 may be overlaid on a graphicalrepresentation of the tibia 70 to which the tibial implant 10 will besecured. For example, as shown in FIGS. 5A-D, a computer monitor orother visual medium may display tibia 70 in different views, for examplea transverse view (FIG. 5A), a perspective view (FIG. 5B), a coronalview (FIG. 5C), and a sagittal view (FIG. 5D). These views may bedisplayed separately or together in any combination. Each view of thetibia 70 may be based on data obtained from medical imaging, for examplean X-Ray or CT scan. In particular, it is preferable that the medicalimaging data includes physiological information of the tibia 70, such asabsolute or relative bone density information. For example, as best seenin FIGS. 5C-D, tibia 70 may be displayed with a range of shading orcolor, such that a relative high-density portion of the tibia 70, suchas the cortical shell 72, is discernable from a relative low-densityportion of the tibia 70, such as the cancellous core 74. By overlaying agraphical representation of the tibial implant 10 on a graphicalrepresentation of the tibia 70, a surgeon may be able to determinewhether certain sizes and/or positions of screw 50 may be unacceptable,for example because the screw 50 would be positioned too close to thecortical shell 72. For example, a screw 50 coupling the baseplate 20 tothe tibia 70 preferably does not exit the bone at any point.

In an exemplary surgical procedure employing the concepts disclosedherein, a patient that has been determined to require a unicondylartibial implant 10 undergoes medical imaging, for example, a CT or MRIscan. Data from the medical imaging may be used to create a model of thebone if desired. As shown in FIG. 6, one or more views of a graphicalrepresentation of the tibia 70 are displayed on a visual medium, such asa computer monitor 110, for the surgeon to review. The surgeon maysimulate a planned bone resection 76, for example as shown in FIG. 5B.In a unicondylar tibial implantation procedure, the planned boneresection may be a proximal substantially planar resection 76 of themedial or lateral condyle. Viewing the tibial bone that will remainafter the planned resection 76 is made may assist the surgeon indetermining the quality of the bone with which the baseplate 20 andscrew 50 will interact.

With the graphical representation of the tibia 70 displayed on monitor110, the surgeon may select a model of the tibial implant 10. Forexample, one or more models of tibial implants may be stored in thememory 120 of a computer 100 in communication with the monitor 110. Thememory 120 may include, for example, standard or non-standard sizes ofavailable medial or lateral tibial implants 10. The surgeon selects thedesired tibial implant 10, and, with the aid of processor 130, a modelof the tibial implant 10 may be displayed on monitor 110 and overlaid onthe graphical representation of the tibia 70. The surgeon may translateand/or rotate the model of the tibial implant 10 to a desired operativeposition on the graphical representation of the tibia 70. Each modeltibial implant 10 may include a combination of model volumes whichcorrespond to volumes that may be occupied by one or more sizes ofscrews 50 for use in securing the baseplate 20 to the tibia 70. Forexample, as shown in FIGS. 5C-D, the model of the tibial implant 10 mayinclude representations of volumes 52A-C corresponding respectively tothe volume that may be occupied by screws 50 having lengths of 15 mm, 25mm, and 35 mm.

As the surgeon translates and/or rotates the model of the tibial implant10 through a variety of positions, the volumes 52A-C movecorrespondingly to show the surgeon the entire range of possiblepositions that a screw 50 securing the baseplate 20 to the tibia 70 mayoccupy. Viewing the position of the model tibial implant 10 and possiblepositions of a variety of screws 50 with respect to the geometry oftibia 70, as well as physiological bone properties illustrated in themodel tibia 70, the surgeon may choose the optimum or desiredcombination of placement of tibial implant 10 on tibia 70, as well assize, shape, and orientation of screw 50 to secure the baseplate 20 tothe tibia. For example, for a given position of tibial implant 10, thesurgeon may determine a desired length and orientation of screw 50 toensure the planning of the screw 50 maintains a desired distance fromthe cortical shell 72 and is also positioned, for example, in bonehaving good quality, as determined by the bone density mapped onto therepresentation of tibia 70.

Although the above described procedure may be performed pre-operativelyor intra-operatively, it is preferable for the planning to occurpre-operatively. Once the surgeon has determined the desired placementof tibial implant 10 and position and size/shape of screw 50, thesurgeon may begin the procedure. The surgeon may utilize navigationsystems to facilitate the procedure. Surgical navigation systems aredescribed in greater detail, for example, in U.S. Pat. No. 7,725,162,the contents of which are hereby incorporated by reference herein. Inone example, a registration tool may be used to register landmarks ofthe patient's tibia to a navigation system, and trackers may be providedon the tibia and/or tools used in the procedure so that a computermonitor or other display device can display in real-time or nearreal-time the position of the tibia 70 and the position of surgicaltools as they move in relation to the tibia 70. The navigation systemmay be combined with the screw trajectory planning to help ensure thatthe screw 50 is implanted in a desired position, as described in greaterdetail below.

Once registered, tibia 70 in the operating room (shown in FIG. 7A) maybe simultaneously represented on a graphical display (shown in FIG. 7B).The graphical representation of tibia 70 may be the same as that chosenby the surgeon during the pre-operative planning, for example as shownin FIG. 5C. Thus, the representation of the tibia 70 used duringnavigation may include the model tibial implant 10 and one or morevolumes 52A-C that screw 50 may occupy. When drilling a pilot hole intothe tibia 70 for screw 50 (or otherwise directly drilling screw 50 intothe tibia 70 without a pilot hole), a drill 200 may be used by thesurgeon. The drill 200 may be registered to the navigation system, forexample by trackers 210. Thus, as the drill 200 is driven into the tibia70 (shown in FIG. 7A, a representation of the drill 200 and its positionrelative to the tibia 70 is provided on the navigation system (shown inFIG. 7B). With this feature, the surgeon is able to confirm in real timethat the drill 200 and/or the screw 50 being inserted into tibia 70 ispositioned mostly or entirely within the appropriate volume 52A-C chosenduring pre-operative planning.

During the implant procedure, portions of one or more volumes 52A-C maybe provided with further indicia to aid the surgical procedure. Forexample, a highly desirable volume within the volumes 52A-C may be colorcoded green, a less desirable volume within the volumes 52A-C may becolor coded yellow, and a least desirable volume within the volumes52A-C may be color coded red. With this feature, the surgeon may beprovided with further guidance to help increase the accuracy with whichthe surgeon is able to place the screw 50 into the desired volume ofbone. It should be understood that the color coding system providedabove is merely an example, and other indicia may be used.

Although the tibial implantation procedure above is described as amanual procedure utilizing the pre-operative planning, the conceptsdescribed herein are not so limited. For example, the position of thetibial implant 10 chosen pre-operatively, as well as the desiredposition of a particular screw 50, may be input into the navigationsystem as described above, with the navigation system operably coupledwith a partially or fully automated surgical system. For example, thenavigation system may be coupled to a robotic arm with a drillattachment. The robotic arm may utilized the preoperative data to drillscrew 50 into tibia 70, with the drilling confined to the appropriatevolume 52A-C chosen during preoperative planning Alternately, the robotmay be partially automated. For example, the data for volume 52A-C maybe utilized to provide boundaries for a drill, for example attached to arobotic arm, with the robotic arm and drill being manually controlled bythe surgeon. As the surgeon uses the robotic arm and drill attachment todrill the pilot hole (or to directly drill the screw 50 into the tibia70), the surgeon may move the drill within the pre-defined volume 52A-C,with the robot inhibiting movement of the drill outside that pre-definedvolume. Effectively, this partially automated system allows the surgeonfull manual control of drilling within the pre-defined volume 52A-C, andeliminates the ability of the surgeon to drill outside the pre-definedvolume 52A-C.

One embodiment of the inventive method has been described above inrelation to screw size, shape, position, and/or orientation planningwith respect to the implantation of a unicondylar tibial implant system10 onto a bone using a single screw 50. However, as noted above, theplanning methods are not so limited. For example, the planning methodsmay be used in planning and/or carrying out the implantation of a boneplate 310 onto a long bone, such as the humerus 370. As shown in FIG.8A, the humerus 370 is a long bone of the arm with a head 372 thatarticulates in the glenoid cavity of the scapula. When the head 372 ofthe humerus 370 breaks, one method of treatment may be fixing a boneplate 310 to the head 372 and along the shaft of the humerus 370. Asshown in FIG. 8B, bone plate 310 may include a first, relativelystraight narrow shaft portion 312 and a larger, rounded head portion 314angled with respect to the shaft portion 312. The shaft portion 312 ofbone plate 310 may be configured for coupling to the shaft of thehumerus 370, with the head portion 314 configured for coupling to thehead 372 of the humerus 370. A number of apertures 316 may be positionedalong the bone plate 310, the apertures 316 configured to receive bonescrews or pegs to couple the bone plate 310 to the humerus 315.

As shown in FIG. 8C, the bone plate 310 may be attached to the humerus370 with a plurality of fasteners. Although the fasteners are shown asbones screws 350, one or more of the fasteners may take the form of abone pin, which may be unthreaded with a relatively blunt tip.Generally, the bone screws 350 in coupling the shaft 312 of the boneplate 310 to the shaft of the humerus 370 may be generally parallel toone another and orthogonal to the bone. The bone screws 350 coupling thehead 314 of the bone plate 310 to the head 372 of the humerus 372 may benonparallel relative to one another. The position and orientation of thefasteners in the connected the head 314 of the bone plate 310 to thehead 372 of the humerus 370 may be indicated by the deformity in thehead 372 of the humerus 370. However, the position of one particularbone screw 350 in the head 372 of the humerus 370 may also be dependenton the position of other bone screws 350 in the head 372 of the humerus370. For example, care must be taken to ensure that a first bone screw350 in the head 372 of the humerus 370 does not interfere with otherbone screw 350 positioned nearby. The screw planning described above maybe useful in planning the implantation of bone plate 310 onto humerus370, as described in greater detail below.

Referring to FIG. 8D, a model of a bone plate 310 may be positioned on amodel of the humerus 370 in a desired implant position. The model of thebone plate 310 may include volumes 352A-C that a first bone screw 350may occupy, with the different volumes 352A-C corresponding to differentsizes/shapes of the bone screw. Similarly, the model of the bone plate310 may include volumes 352D-F that a second bone screw 350 may occupy,with the different volumes 352D-F corresponding to differentsizes/shapes of the bone screw. The volumes 352A-C and 352D-F may beused in the same or similar manner as described with respect to thetibial implantation procedure described above to ensure that the bonescrews 350 are not positioned too close to the edge of the humerus 370,and do not exit the bone.

In addition to appropriately positioning the bone screws 350 withrespect to the anatomy, the screw planning may additionally be used toavoid interference between the bone screws 350. For example, inpre-operative planning similar to that described above in relation tothe tibial implantation procedure, the computer displaying the volumes352A-C and 352D-F may indicate a volume of interference 354. As shown inFIG. 8E, the volume of interference 354, shown as hatched lines,illustrates a volume of overlap between one or more of volumes 352A-Cwith one or more of volumes 352D-F. Either as part of the pre-operativeplanning, or during intra-operative navigation utilizing the screwplanning, the surgeon may ensure that one or both screws 350 beinginserted into the head 372 of humerus 370 avoid the volume ofinterference 354. In a two screw system, as long as one of the screws350 does not occupy space of the volume of interference 354, thepossibility of those screws contacting one another is eliminated.Similarly, if more than two screws are used with potential interference,it may be preferable for all screws to avoid any indicated volume ofinterference. Finally, a buffer volume may be added to the volume ofinterference 354 so to provide a minimum distance between two nearbybone screws 350, as it may be undesirable to have two bone screws 350very close to one another, even if they do not contact one another.Otherwise, the pre-operative planning and intraoperative navigationusing the screw trajectory planning in relation to the tibialimplantation described above apply with equal force to the implantationof a bone plate 310 on a bone.

Finally, as noted above, the implant size, shape, position, and/ororientation planning described herein may be used with any implantsystem in which an implant is being implanted into the body relative toanother implant or anatomical structure. As should be clear from theexamples described above, the methods described herein may beparticularly useful when that bone (or another implant device) providelimitations on the size, shape, position, and/or orientation of theimplant device being implanted into the patient. Another example whereimplant position, size, shape and/or orientation planning may be usefulis with acetabular shells of hip implants. For example, an acetabularshell may take the form of a hollow, hemispherical implant with aplurality of apertures therein used to screw the acetabular shell intothe acetabulum. The concepts described above may be implemented in a hipimplantation procedure to ensure that screws or other fasteners couplingthe acetabular shell to the acetabulum are positioned desirably withrespect to the existing anatomy. The selection of the number, size,shape, position, and/or orientation of the fasteners may also oralternatively be dependent upon a desired position, sizing, and/ororientation of the acetabular shell. It should be clear that theinventive methods may be applied to other exemplary implant procedures,some of which are briefly described below.

In total knee arthroplasty (“TKA”) procedures, a femoral component of aprosthesis system is implanted onto the distal femur. In some cases,whether a primary implant or a revision, the femoral component isanchored to the femur with another component, such as a femoral stemthat is coupled to the femoral component and extends into anintramedullary canal created (or already existing from a priorimplantation) in the femur. The inventive methods described above may beapplied to planning the size, shape, position, and/or orientation of thefemoral stem relative to the femur. The size, shape, position, and/ororientation of the stem may include similar limitations as describedabove in relation to screws being implanted into the tibia during a PKA.For example, it may be desirable to plan the size, shape, position,and/or orientation of the stem component so that a preferred or at leasta minimum thickness of bone exists around the circumference or on allsides of the stem. In addition, the planning may take into account thedensity or other quality of the bone to determine a desired size, shape,position, and/or orientation of the implant within the bone. The methodsdescribed above are readily adaptable to planning the size, shape,position and/or orientation of the stem in relation to the femur so thata desired position is obtained, which may include pre-operative and/orintraoperative planning and navigation. In other TKA procedures,particularly in revision procedures, a femoral augment may first beimplanted into the femur to facilitate the later implantation of thefemoral component and/or its corresponding stem. In these cases, themethods described above may be adapted to planning the size, shape,position, and/or orientation of the femoral augment into the femur.Similarly, in some implant systems, a tibial component may include astem and/or augment for providing support to the implanted tibialcomponent. The methods described above may be similarly applied toplanning the size, shape, position, and/or orientation of augmentsand/or stems of tibial components of an implant system with respect tothe tibial component and/or tibial anatomy. Procedures for implantingfemoral components, including corresponding stems and/or augments, aredescribed in greater detail in U.S. Pat. No. 9,011,444 and U.S. PatentPublication No. 2014/0277567, the disclosures of which are both herebyincorporated by reference herein.

Similar to the TKA procedures described above, primary or revisionprosthetic hip implantation procedures, in addition to the acetabularshell described above, may include a prosthetic femoral head toarticulate with respect to the acetabular shell. Generally, theprosthetic femoral head is attached to a neck or body portion which isattached to a femoral stem extending into an intramedullary canal in thefemur to provide support to the prosthetic femoral head in a mannersimilar to stems used in connection with femoral components ofprosthetic knee implant systems. Based on the geometric center of theprosthetic femoral head and/or the existing femoral anatomy, theposition, size, shape and/or orientation of the femoral stem may beplanned pre-operatively and/or intraoperatively using methods similar tothose described above. Some hip implant systems may be modular, with theneck or body portion separately coupled to the femoral stem. With suchmodular systems, different neck or body portions may be chosen by thesurgeon to provide a different offset distance between the geometricalcenter of the prosthetic femoral head and the longitudinal center of thestem. The particular offset in the prosthetic hip system chosen may bean additional or alternative basis for planning the size, shape,position, and orientation of the stem in the femur.

Another type of procedure that may benefit from the use of the methodsdescribed above is an osteotomy, such as a high tibial osteotomy(“HTO”). Generally, in an HTO procedure, one or more cuts are made inthe tibia, in the vicinity proximal (or below) the proximal end of thetibia. The cuts may be performed to shorten or lengthen a portion of thetibia. For example, if a patient has arthritis on the lateral portion ofa knee joint, with the medial knee joint being relatively healthy, anHTO may be performed on the medial side of the tibia, with a wedge ofbone being removed, to shift more weight onto the healthy medial kneejoint and divert weight from the arthritic medial knee joint. Generally,a wedge of bone may be removed to shorten the side of the tibia with thebone removed (closing wedge osteotomy) or a cut may be made with a wedgeof bone (autograft or allograft) or other biocompatible materialinserted into the cut to lengthen the side of the tibia with the boneadded (opening wedge osteotomy). Following the osteotomy, a bone plateor other fixation device may be coupled to the bone around the osteotomywith screws or other fasteners to facilitate long term healing of thebone. In either case, when fixing the bone plate to the bone followingosteotomy, the methods described above may be employed to plan screwsize, shape, position, and/or orientation in a similar manner asdescribed in connection with FIGS. 8A-E. In other words, the size,shape, position, and/or orientation of the screws may be planned basedon the anatomy and/or the geometry and features of the particularfixation plate. In addition, for opening wedge osteotomies, such as anopening wedge HTO, the size, shape and/or position of the wedge insertedinto the osteotomy may be used as an additional factor for planning thesize, shape, position, and/or orientation of the screws (or otherfasteners) coupling the associated bone plate to the bone. In oneexample, it may be desirable to insert fasteners through the fixationplate so that they avoid the implanted wedge, preferably with a bufferdistance between the implanted wedge and any fasteners fastening thefixation plate to the bone. However, in other examples, it may bedesirable to place fasteners through the wedge, with or without thefastener extending into bone. Certain types of osteotomy procedures aredescribed in greater detail in U.S. Pat. No. 8,241,292, the disclosureof which is hereby incorporated by reference herein.

Still other procedures that may employ the inventive concepts describedabove include spinal implants. For example, in some patients, it isdesirable to fuse adjacent vertebrae together. For example, some implantsystems include a cage, device, plate or other structure positionedwithin adjacent vertebral bodies, in the intervertebral space betweenadjacent vertebral bodies or on an outer surface of the vertebralbodies. At least one screw extending through the implant systems andinto a first vertebral body, and with at least one screw extendingthrough the implant systems and into a second vertebral body adjacentthe first. With this configuration, each vertebral body on either sideof the cage, device or plate, for example, becomes positionally fixedrelative to one another. Generally, the cortical shell of the vertebralbody is relatively hard compared to the softer cancellous bone inside.One or both of the prosthetic implant and the anatomy of the vertebralbodies, such as two adjacent vertebral bodies on either side of theprosthetic implant, may be taken into account to plan the size, shape,position, and/or orientation of any fasteners, such as screws, couplingthe prosthetic implant to the adjacent vertebral bodies. For example, itmay be desirable for a certain distance buffer zone to exist between theposterior cortical shell of each vertebral body and any screw or otherfastener passing into that vertebral body. Also, similar to embodimentsdescribed above, when more than one fastener is used in any particularvertebral body, planning may help ensure that fasteners do notunintentionally contact one another.

Other spinal procedures may also benefit from incorporating theinventive concepts described above into the spinal procedure. Forexample, another type of spinal fusion procedure, as an alternative orin addition to the type described directly above, includes implantingpedicle screws into the pedicle bone on the posterior spine and throughthe vertebral body. Generally, one pedicle screw is positioned throughthe pedicle on each side of the spine, the screws extending anteriorly,for example, into the vertebral body. This is in contrast to the spinalsystems described above, in which screws generally extend posteriorlyinto the vertebral body. The size, shape, position, and/or orientationof the pedicle screws may be planned using methods similar to thosedescribed above, for example to facilitate proper placement through boneand to avoid the spinal cord, and further to keep a distance bufferbetween the screws and the posterior cortical shell of the vertebralbody or any other screws positioned within the vertebral body. Stillfurther, once the pedicle screws are implanted in two or more adjacentvertebral bodies, a rigid element such as a rod is placed withinposterior head portions of the pedicle screws, effectively coupling twoor more pedicle screws in series on one side of the spine, with asimilar element such as a rod connecting two or more pedicle screws inseries on the other side of the spine. This configuration fusesvertebral bodies coupled together via the rod extending along adjacentpedicle screws passing into the vertebral bodies. In cases in which aparticular bend or curvature of the rod is desired, the pedicle screwsize, shape, position and/or orientation may be planned to account forthe desired rod curvature. For example, because the rod traversesthrough proximal head portions of adjacent pedicle screws, the curvatureof the rod will be determined, at least in part, by the position of theposterior heads of each pedicle screw in the relevant series. To attaina particular rod curvature, the sizes, shapes, positions, and/ororientations of each pedicle screw in a particular series may be plannedso that the posterior head of each pedicle screw is in a desiredposition and orientation to provide the desired curvature of a rodpassing through the series of posterior pedicle screw heads.

Although planning of size, shape, position and/or orientation of boneplate fasteners is described in detail above, for example in connectionwith FIGS. 8A-E, it should also be understood that the planning methodsdescribed herein may be particularly effective when coupling a boneplate to a comminuted fracture. Generally, a comminuted fracture is afracture in which the bone is broken into several pieces. In order toeffectively fix the several broken pieces relative to one another with abone plate or other similar device, precise placement and number offasteners through the bone plate and into the bone may be required. Theplanning methods described above may be employed in comminuted fracturefixation with a bone plate to help ensure that the size, shape,position, and/or orientation of fasteners coupling the bone plate to thebone secure the several pieces of bone desirably relative to oneanother.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A surgical method comprising: displaying on a display device a modelof a bone; displaying on the display device a first boundary area of afirst fastener configured to pass into the bone, wherein the firstfastener has a plurality of separately and independently viablepositions, the first boundary area simultaneously representing a rangeof all the plurality of separately and independently viable positionsthat the first fastener may have when the first fastener is implanted inthe bone; displaying on the display device a second boundary area of asecond fastener configured to pass into the bone, wherein the secondfastener has a plurality of separately and independently viablepositions, the second boundary area simultaneously representing a rangeof all the plurality of separately and independently viable positionsthat the second fastener may have when the fastener is implanted in thebone; determining whether the first boundary area and the secondboundary area have a volume of interference in which the first fastenerwould interfere with the second fastener; and implanting the firstfastener and second fastener into the bone so that the first fastenerdoes not contact the second fastener.
 2. The surgical method of claim 1,further comprising displaying on the display device the volume ofinterference.
 3. The surgical method of claim 1, further comprisingproviding a buffer volume in addition to the determined volume ofinterference so as to provide for a minimum distance between the firstfastener and the second fastener when the first fastener and the secondfastener are implanted into the bone, the minimum distance being greaterthan zero.
 4. The surgical method of claim 1, further comprising settinga minimum distance between the first fastener and the second fastener,the minimum distance being greater than zero.
 5. The surgical method ofclaim 1, wherein displaying the model of the bone includes displayingbone quality information on the model of the bone.
 6. The surgicalmethod of claim 6, wherein the bone quality information is bone density.7. The surgical method of claim 1, further comprising displaying on thedisplay device a model of an implant having a first aperture forreceiving the first fastener and a second aperture for receiving thesecond fastener.
 8. The surgical method of claim 7, further comprisingpositioning the model implant on the model bone in a desired implantposition on the display device.
 9. The surgical method of claim 8,wherein the implant is a bone plate.
 10. The surgical method of claim 8,wherein the first boundary area is displayed with the first fastenerfully received within the first aperture, and the second boundary areais displayed with the second fastener fully received within the secondaperture.
 11. The surgical method of claim 1, wherein the displayedfirst boundary area has a plurality of area portions such that each areaportion simultaneously represents all possible positions of a differentsized first fastener.
 12. A computer system including a memory and aprocessor configured to execute instructions stored in the memory to:display on a display device a model of a bone; display on the displaydevice a first boundary area of a first fastener configured to pass intothe bone, wherein the first fastener has a plurality of separately andindependently viable positions, the first boundary area simultaneouslyrepresenting a range of all the plurality of separately andindependently viable positions that the first fastener may have when thefirst fastener is implanted in the bone; display on the display device asecond boundary area of a second fastener configured to pass into thebone, wherein the second fastener has a plurality of separately andindependently viable positions, the second boundary area simultaneouslyrepresenting a range of all the plurality of separately andindependently viable positions that the second fastener may have whenthe fastener is implanted in the bone; and indicate whether the firstboundary area and the second boundary area have a volume of interferencein which the first fastener would interfere with the second fastener.13. The system of claim 12, wherein indicating whether the firstboundary area and the second boundary area have a volume of interferenceincludes displaying on the display device the volume of interference.14. The system of claim 13, wherein the processor is further configuredto provide a buffer volume in addition to the volume of interference soas to provide for a minimum distance between the first fastener and thesecond fastener when the first fastener and the second fastener areimplanted into the bone, the minimum distance being greater than zero.15. The system of claim 12, wherein the processor is further configuredto set a minimum distance between the first fastener and the secondfastener, the minimum distance being greater than zero.
 16. The systemof claim 12, wherein the processor is further configured to display bonequality information on the model of the bone.
 17. The system of claim16, wherein the bone quality information is bone density.
 18. The systemof claim 12, wherein the processor is further configured to display onthe display device a model of an implant having a first aperture forreceiving the first fastener and a second aperture for receiving thesecond fastener.
 19. The system of claim 18, wherein the implant is abone plate.